Bài 7:
a: \(=31\left(-18-81-1\right)=31\cdot\left(-100\right)=-3100\)
b: \(=\left(-12\right)\cdot\left(47+52+1\right)=-12\cdot100=-1200\)
c: \(=13\cdot45-3\cdot45=45\cdot10=450\)
d: \(=-48\left(1+78+21\right)=-48\cdot100=-4800\)
e: \(=135\cdot171-135\cdot123-171\cdot135+171\cdot123\)
\(=123\left(171-135\right)=123\cdot36=4428\)
g: \(=2009-97-2009-3+74\cdot18-74\cdot118\)
\(=74\cdot\left(-100\right)+\left(-100\right)=75\cdot\left(-100\right)=-7500\)